Method and apparatus for generating and transmitting code sequence in a wireless communication system

ABSTRACT

A method of generating a code sequence in a wireless communication system is disclosed. More specifically, the method includes recognizing a desired length of the code sequence, generating a code sequence having a length different from the desired length, and modifying the length of the generated code sequence to equal the desired length. Here, the step of modifying includes discarding at least one element of the generated code sequence or inserting at least one null element to the generated code sequence.

This application is a continuation of U.S. application Ser. No.11/563,909, filed Nov. 28, 2006, now U.S. Pat. No. 7,746,916, whichclaims the benefit of Korean Application No. P2005-114306, filed on Nov.28, 2005, Korean Application No. P2006-62467, filed on Jul. 4, 2006, andKorean Application No. P2006-64091, filed on Jul. 7, 2006, which are allhereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of generating and transmittingcode sequence, and more particularly, to a method and apparatus forgenerating and transmitting code sequence in a wireless communicationsystem.

2. Discussion of the Related Art

Usually, a pilot signal or a preamble of a wireless communication systemis referred to as a reference signal used for initial synchronization,cell search, and channel estimation. Further, the preamble is comprisedof a code sequence, and the code sequence is further comprised oforthogonal or quasi-orthogonal which represent good correlationproperties.

For example, a Hadamard matrix of 128×128 is used in a portable internet(PI) to insert the code sequence to the frequency domain. In so doing,127 types of code sequences are used.

Although the Hadmard code sequence and a poly-phase Constant AmplitudeZero Auto-Correlation (CAZAC) code sequence are orthogonal codes, anumber of codes used to maintain orthogonality is limited. For example,a number of N orthogonal codes in a N×N Hadamard matrix is N, and anumber of N orthogonal codes that can be expressed by the CAZAC codes isN and a prime number smaller than N (David C. Chu, “Polyphase Codes withGood Periodic Correlation Properties,” Information Theory IEEETransaction on, vol. 18, issue 4, pp. 531-532, July 1972). With respectto CAZAC sequence types, GCL CAZAC and Zadoff-Chu CAZAC are often used.

If the code sequence is generated using the Hadamard codes, N number ofsequence types corresponding to the entire length of the codes isgenerated. However, the if the code sequence is generated using theCAZAC codes, only half or N/2 number of sequence types are generated.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method and apparatusfor generating and transmitting code sequence in a wirelesscommunication system that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of generatinga code sequence in a wireless communication system.

Another object of the present invention is to provide an apparatus forgenerating a code sequence in a wireless communication system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of generating a code sequence in a wireless communication systemincludes recognizing a desired length of the code sequence, generating acode sequence having a length different from the desired length, andmodifying the length of the generated code sequence to equal the desiredlength. Here, the step of modifying includes discarding at least oneelement of the generated code sequence or inserting at least one nullelement to the generated code sequence.

In another aspect of the present invention, method of generating a codesequence in a wireless communication system includes a recognizing adesired length of a first code sequence, generating a second codesequence having a length different from the desired length of the firstcode sequence, and modifying the length of the second code sequence toequal the desired length of the first code sequence. Here, the step ofmodifying includes discarding at least one element of the modified codesequence if the length of the modified code sequence is longer than thedesired length of the first code sequence or inserting at least one nullelement to the modified code sequence if the length of the modifiedsecond code sequence is shorter than the desired length of the firstcode sequence.

In a further aspect of the present invention, an apparatus forgenerating a code sequence in a wireless communication system includes asequence selection unit for recognizing a desired length of the codesequence, generating a code sequence having a length different from thedesired length, and modifying the length of the generated code sequenceto equal the desired length, wherein the sequence selection unitdiscards at least one element of the generated code sequence or insertsat least one null element to the generated code sequence in modifyingthe length of the generated code sequence, and a transmitting unit fortransmitting the modified generated code sequence via at least oneantenna.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 illustrates a structure of an apparatus for transmitting datausing Orthogonal Frequency Division Multiplexing (OFDM) or OFDM Access(OFDMA) scheme;

FIG. 2 illustrates a structure of an apparatus for receiving data usingOFDM/OFDMA scheme;

FIG. 3 is a flow diagram illustrating adjusting a code sequence;

FIG. 4 illustrates cross-correlation properties of the generated codesequence;

FIG. 5 illustrates a generated CAZAC sequence ^(a)N_(seq) _(—) _(N)xNusing N (=1024);

FIG. 6 illustrates a cross-correlation properties cumulativedistribution function (CDF) of the code sequences that can be generatedaccording to the code sequence ^(a)N_(seq) _(—) _(N)xN and the CAZACsequence ^(a)N_(seq) _(—) _(N)xN when N=1024;

FIG. 7 illustrates the cross-correlation properties CDF of the codesequences that can be generated based on the CAZAC sequence generatedusing the prime number of N=1031 and a code sequence set ^(a)N_(seq)_(—) _(N)xN having length of 1024 (seven (7) elements removed);

FIG. 8 illustrates a method of generating CAZAC sequence using a lengthrequired by a communication system;

FIG. 9 illustrates a method of generating a CAZAC sequence using apadding portion;

FIG. 10 illustrates an exemplary application of circular shift;

FIG. 11 is an exemplary diagram illustrating application of circularshift to the generated code sequence after the elements of the codesequence are removed;

FIG. 12 is an exemplary diagram illustrating application of circularshift to the generated code sequence prior to removing the elements ofthe code sequence;

FIG. 13 is an exemplary diagram illustrating application of circularshift to the generated code sequence after a padding portion isattached;

FIG. 14 is an exemplary diagram illustrating application of circularshift to the generated code sequence prior to attaching a paddingportion;

FIG. 15 is an exemplary diagram of a padding portion of the codesequence in which the padding portion is used as a lower bandwidth guardinterval;

FIG. 16 is a structural diagram for transmitting the code sequence.Depending on whether the transmission of the code sequence is made in adownlink direction or an uplink direction, the structure can be indifferent form;

FIG. 17 is a structural diagram illustrating a basic code sequencegeneration unit and a code sequence length adjustment unit;

FIG. 18 illustrates cross-correlation characteristics of the codesequence;

FIG. 19 illustrates cross-correlation characteristics of the codesequence; and

FIG. 20 is an exemplary diagram illustrating boosting the power of thegenerated code sequence.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 illustrates a structure of an apparatus for transmitting datausing Orthogonal Frequency Division Multiplexing (OFDM) or OFDM Access(OFDMA) scheme. FIG. 2 illustrates a structure of an apparatus forreceiving data using OFDM/OFDMA scheme.

In FIG. 1, traffic data and control data are multiplexed at a muxer 11.Here, the traffic data is used to provide service from a transmittingend to a receiving end, and the control data is used to facilitatetransmission from the transmitting end to the receiving end. Thediscussion relating to the present invention regarding the code sequencewhich relates to a type of a code sequence of the control data. The codesequence can be used for initial synchronization, cell search, orchannel estimation.

Depending on the communication system, the code sequence can be used invarious forms. For example, the code sequence in an IEEE 802.16 widebandwireless access system can be used in a preamble or a pilot signalformat, and in a multi-input, multi-output (MIMO) system, the codesequence can be used as a midamble format.

After being processed at the muxer 11, the multiplexed traffic andcontrol data is then channel coded by a channel coding module 12.Channel coding is used to allow the receiving end to correct error thatcan occur during transmission by adding parity bits. Examples of channelcoding include convolution coding, turbo coding, and low density paritycheck (LDPC) coding.

Thereafter, the channel coded data is modulated by a digital modulationmodule 13 in which data symbols are mapped using algorithms such as aquadrature phase shift keying (QPSK) or a 16-quadrature amplitudemodulation (16QAM). The mapped data symbols are then processed by asubchannel modulation module 14 through which the data symbols aremapped to each subcarrier of the OFDM system or OFDMA system. Then, thedata symbols mapped to subcarriers are processed by an inverse fastFourier transform (IFFT) module 15 which transform the data symbols intoa signal in a time domain. The transformed data symbols are thenprocessed through a filter 16 and further processed through adigital-to-analog conversion (DAC) module 17 where the filtered datasymbols are converted to analog signals. Lastly, the analog signals areconverted into a radio frequency (RF) by a RF module 18 which is thentransmitted via an antenna 19 to the receiving end.

Based on the type of generated code (e.g., CAZAC code), the steps ofchannel coding and/or symbol mapping can be omitted. FIG. 2 illustratesa receiving end whose processes are inverse to those of the transmittingend.

A code sequence is used for transmitting control information, whichincludes identification (ID) and synchronization information, toclassify types of sequences in a communication system. In order for moreeffective reception of the control information using code sequence, thecode sequence can be adjusted or modified. Further, the code sequencecan be applied to all of the channels that use code sequence for controlsignaling such as a random access channel (RACH), downlink/uplinkreference symbol, channel quality information (CQI), and Acknowledgement(ACK)/Negative Acknowledgement (NACK).

FIG. 3 is a flow diagram illustrating adjusting a code sequence. Morespecifically, a length of the code sequence is defined as N, a number ofcodes in the code sequence is defined as ^(N) _(seq) _(—) _(N), and acode sequence set defined as ^(a)N_(seq) _(—) _(N)xN. In operation, thecode sequence set ^(a)N_(seq) _(—) _(N)xN having ^(N) _(seq) _(—) _(N)number of codes can be extended to a code sequence set ^(a)N_(seq) _(—)_(N)xN having ^(N) _(seq) _(—) _(M) number of codes.

Equation ^(a)N_(seq) _(—) _(N)xN is a matrix of ^(N) _(seq) _(—) _(N)^(x)N of

a_(N_(seq_N)xN) = [a_(N_(seq_N)xN)⁰a_(N_(seq_N)xN)¹  …  a_(N_(seq_N)xN)^(N_(seq) − 1)]^(T),  and  a_(N_(seq_N)xN)^(k)is a row vector of

a_(N_(seq_N)xN)^(k) = ⌊a_(N_(seq_N)xN)^(k)(0)a_(N_(seq_N)xN)^(k)(1)  …  a_(N_(seq_N)xN)^(k)(N − 1)⌋.Furthermore,

a_(N_(seq_N)xN)^(k)(n)(n) indicates n(=0,1,2, . . . , element of k(=0,1,2, . . . , N_(seq)_(—) _(N)−1) code sequence.

Referring to FIG. 3, a code sequence set ^(a)N_(seq) _(—) _(N)xM, having^(N) _(seq) _(—) _(M) number of code sequence(s) where each codesequence has length M, can be generated based on the code generationalgorithm based on code type in which a value of length M is a naturalnumber greater than a value of length N (S301). Here, the code typesinclude Hadamard code, Pseudo Noise (PN) code, and a Constant AmplitudeZero Auto-Correlation (CAZAC) code, among others to be used for initialsynchronization, cell search, and channel estimation in the wirelesscommunication system. The code sequence set having length M per eachcode type can be generated by various schemes as discussed. As for theCAZAC code, the value of length M is a smallest prime number greaterthan the value of length N, preferably.

Subsequently, a code sequence set ^(a)N_(seq) _(—) _(N)xN having ^(N)_(seq) _(—) _(M) number of code sequences, can be generated where aresulting length of the code sequence is length N. More specifically,the code sequence set ^(a)N_(seq) _(—) _(N)xM having ^(N) _(seq) _(—)_(M) number of code sequences where each code sequence has length M(from step S301), can have elements of the code sequence removed. Thatis, elements which comprise each code sequence can be removed from thecode sequence allowing the length of the code sequence to be adjusted orshortened. Here, M−N number of elements can be removed from the codesequence whose length corresponds to length M. By removing elements fromthe code sequence with length M, a code sequence having length N can begenerated. As discussed, N is smaller than M.

Consequently, a code sequence set ^(a)N_(seq) _(—) _(N)xN having ^(N)_(seq) _(—) _(M) number of code sequences in which each code sequencehas length N, can be generated (S302).

A code sequence is used for transmitting control information, whichincludes identification (ID) and synchronization information, toclassify types of sequences in a communication system. Currently in3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE),a CAZAC sequence is being considered.

The CAZAC sequence can be used by channels to output various IDs andinformation. The channels include channels for downlink synchronization(e.g., primary synchronization channel, secondary synchronizationchannel, and broadcast channel), uplink synchronization (e.g., randomaccess channel), and pilot channels (e.g., data pilot and channelquality pilot). Further, the CAZAC sequence can be used in scrambling aswell as channels that use code sequence such as RACH.

Although there are various types of the CAZAC sequences, there are twotypes of often used CAZAC sequences—GCL CAZAC and Zadoff-Chu CAZAC. TheZadoff-Chu CAZAC sequence can be defined by the following equations.

$\begin{matrix}{{c( {{k;N},M} )} = {{\exp( \frac{{j\pi}\;{{Mk}( {k + 1} )}}{N} )}\mspace{14mu}( {{for}\mspace{14mu}{odd}\mspace{14mu} N} )}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack \\{{c( {{k;N},M} )} = {{\exp( \frac{{j\pi}\;{Mk}^{2}}{N} )}\mspace{14mu}( {{for}\mspace{14mu}{even}\mspace{14mu} N} )}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

Here, k denotes sequence index, N denotes a length of CAZAC to begenerated, and M denotes sequence ID.

If the Zadoff-Chu CAZAC sequence and the GCL CAZAC sequence areexpressed by c(k; N, M) as shown in Equations 1 and 2, then thesequences have the following three (3) characteristics as presented infollowing equations.

$\begin{matrix}{{{c( {{k;N},M} )}} = {1\mspace{14mu}( {{{for}\mspace{14mu}{all}\mspace{14mu} k},N,M} )}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack \\{{R_{M:N}(d)} = \{ \begin{matrix}{1,} & ( {{{for}\mspace{14mu} d} = 0} ) \\{0,} & ( {{{for}\mspace{14mu} d} \neq 0} )\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 4} \rbrack \\{{R_{M_{1},{M_{2};N}}(d)} = {p\mspace{14mu}( {{{for}\mspace{14mu}{all}\mspace{14mu} M_{1}},{M_{2}\mspace{14mu}{and}\mspace{14mu} N}} )}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

According to Equation 3, the CAZAC sequence always has a size of 1, andthe CAZAC sequence of Equation 4 has an auto-correlation functiondenoted by a delta function. Here, the auto-correlation is based oncircular correlation. Further, Equation 5 is a cross-correlation whichis constant if N is a prime number.

If the length to be applied in the wireless communication system forgenerating the CAZAC sequence is denoted by L, a method for generatingthe CAZAC sequence sets N of Equations 1 and 2 to equal L(N=L)—identified as step (1). Step (2) can be identified by a methodwhere a value of N is set to be a prime number greater than a value oflength L for generating the CAZAC sequence.

Referring to the characteristics of the generated CAZAC sequence havinga specified length of L, if L is not a prime number, the generated CAZACsequence can include M=1, 2, . . . L−1 number of codes, some of whichare repeated codes. In other words, the number of different codes isless than L−1 number of codes. On the contrary, if L is a prime number,there is L−1 number of different codes. The above descriptions may alsobe applied to other types of code sequences and are not limited toZadoff-Chu CAZAC sequence.

Further, the following technique has been considered. More specifically,if the length of code to be applied to the system is not a prime number,and there are a large number of codes to be used, a smallest primenumber greater than L was selected. Using the selected prime number, theCAZAC sequence was generated, and discards or removes at least oneelement of the generated CAZAC sequence for use. This technique isdifferent than the technique introduced with respect to step 1.

For example, assume that a number of codes of a CAZAC code sequence (N)is 1024. The following equation can be used to express an algorithm forgenerating a Zadoff-Chu CAZAC code.

$\begin{matrix}{{a^{{index}{(A)}}(n)} = \{ {{{\begin{matrix}{{\exp( {{\mathbb{i}}\;\frac{A\;\pi\;{n( {n + 1} )}}{M}} )},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{odd}} \\{{\exp( {{\mathbb{i}}\;\frac{A\;\pi\; n^{2}}{M}} )},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{even}}\end{matrix}\mspace{79mu}{where}\mspace{14mu} n} = 0},1,2,\ldots\;,{M - 1}} } & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

In Equation 6, A and M are natural numbers, and index (A)(=0,1,2, . . ., N_(seq) _(—) _(M)−1) is an index of A in ascending order. In order toextend the CAZAC sequence where N=1024, a smallest prime number greaterthan 1024 is used. That is, the smallest prime number greater than 1024is 1031. As such, the code sequence set ^(a)N_(seq) _(—) _(N)xM whereM=1031 is applied to Equation 6.

Since M (=1031) is a prime number, ^(N) _(seq) _(—) _(M)=1030.Furthermore, A can be referred to as a seed value used to generate acode sequence maintaining CAZAC properties. If M is a prime number, atotal of M−1 number of code sequences can be generated. In other words,for example, if M=1024, a total of 512 (=1024/2 or N/2) number of codesequences are generated. However, if M=1031, a total of 1030 number ofcode sequences (M−1) are generated. Moreover, the cross-correlationproperties of the generated code sequence are better if M is a primenumber than a composite number.

In order to adjust or modify the CAZAC code sequence set ^(a)N_(seq)_(—) _(N)xM where M=1031 to a code sequence set ^(a)N_(seq) _(—) _(N)xMwhose length is N=1024, M−N number of elements can be removed from indexn=N, . . . , M−1, generating a code sequence set ^(a)N_(seq) _(—)_(N)xN.

In determining the value of M, although the number of code sequences canincrease with increase in value of N, it is preferable to determine thevalue of M based on the code sequence whose length is N that promotesmaintenance of good correlation properties. In case of the CAZAC code,optimum correlation properties can be attained if the value of length Mis the smallest prime number greater than the value of length N.

If the code sequence set ^(a)N_(seq) _(—) _(N)xN generated using lengthN=1024 is compared with the code sequence set ^(a)N_(seq) _(—) _(N)xN, atotal number code sequences of the former can be represented by N/2 or512 (=1024/2) code sequences having an index 0,1,2, . . . , N/2−1(N=1024), and a total number of code sequences of the latter can berepresented by M−1 or 1030 having an index 0,1,2, . . . , M−2 (M=1031).

FIG. 4 illustrates cross-correlation properties of the generated codesequence. More specifically, the cross-correlation properties of ^(a)_(k) N_(swq) _(—) _(M)xN (k=1,2, . . . , N_(seq) _(—) _(M)−1) associatedwith the remaining ^(N) _(seq) _(—) _(M) (1029) code sequences for ^(a)₀ N_(seq) _(—) _(M)xN code sequence of the code sequence set ^(a)N_(seq)_(—) _(N)xN. The figure illustrates this with respect to amplitude, codeindex, and time index.

Further, FIG. 5 illustrates a generated CAZAC sequence ^(a)N_(seq) _(—)_(N)xN using N (=1024). More specifically, the figures illustratecross-correlation properties of ^(a) _(k) N_(swq) _(—) _(M)xN (k=1,2, .. . , N_(seq) _(—) _(M)−1) regarding the remaining ^(N) _(seq) _(—) _(N)(511) code sequences. The figure illustrates this with respect toamplitude, code index, and time index. Between FIG. 4 and FIG. 5, thecross-correlation properties of the generated code sequence of FIG. 4are better.

FIG. 6 illustrates a cross-correlation properties cumulativedistribution function (CDF) of the code sequences that can be generatedaccording to the code sequence ^(a)N_(seq) _(—) _(N)xN and the CAZACsequence ^(a)N_(seq) _(—) _(N)xN when N=1024.

FIG. 7 illustrates the cross-correlation properties CDF of the codesequences that can be generated based on the CAZAC sequence generatedusing the prime number of N=1031 and a code sequence set ^(a)N_(seq)_(—) _(N)xN having length of 1024 (seven (7) elements removed). Theperformance lines of FIGS. 4-7 indicate that the code sequence set withseven (7) elements removed has equivalent cross-correlation propertiescompared to the original code sequence set.

As discussed, the codes in addition to the CAZAC code are available,such as the PN code and the Hadamard code. The discussion with respectto the CAZAC code sequence can also be applied to the PN code and theHadamard code. With respect to the PN code, a modular shift registergenerator is used to generate the code sequences. If a number of shiftregisters generated is represented by N, a code sequence having a lengthof 2^(N)−1 is generated. Thereafter, a value “1” is added to the shiftregister, resulting in a length 2^(N+1)−1, and then, adjust the lengthto equal 2^(N).

With respect to the Hadamard codes, a number of code sequences, whichequal the length of the code sequence, make up a code sequence. However,for example, if M number of code sequences having length N is required(M>N), then M number of code sequences having length M are generated,followed by removing a specified number of elements to make the lengthof the code sequence equal length N.

FIG. 8 illustrates a method of generating CAZAC sequence using a lengthrequired by a communication system. That is, the required (or desired)length of the CAZAC sequence can be represented by length L. Further,the codes types can be extended. However, since a generated codesequence can be truncated or have elements discarded to correspond tothe desired length L, the auto-correlation and cross-correlationproperties of the truncated code sequence can experience deterioration.Similarly, even if a code sequence portion is added/attached to thegenerated code sequence (e.g., zero-padding or cyclic prefix) tocorrespond to the desired length L, the auto-correlation andcross-correlation properties can experience deterioration. Here,auto-correlation properties relate to the auto-correlation value being 1when the delay is 0. Otherwise, the auto-correlation value is 0 when thedelay is a value other than 0. Further, the cross-correlation propertieshaving a constant value is negatively affected.

Assuming that the code sequence having poor auto-correlation andcross-correlation properties are removed, the remaining number of codesequences may be less than L−1.

In order to attain a desired length and a maximum number of CAZACsequence types corresponding to the desired length, a smallest primenumber, X, greater than the desired length, L, (X>L) can be selected.Although the CAZAC sequence can be generated using X due todeterioration of the correlation properties, the correlations propertiesof CAZAC sequence as shown in Equations 4 and 5 cannot be attained.Further, when selecting a length of the generated code sequence, thelength that is nearest to the desired length L which is between asmallest prime number larger than the desired length or a largest primenumber smaller than the desired length can be selected.

Referring to FIG. 8, the generated CAZAC sequence has length X.Thereafter, the generated CAZAC sequence having length X has elements ofthe code sequence removed (or truncated) so as to make the length of thegenerated CAZAC sequence correspond to the desired length L.

FIG. 9 illustrates a method of generating a CAZAC sequence using apadding portion. As discussed, the generated CAZAC sequence istruncated. With respect to auto-correlation and cross correlationproperties, delay of 0 indicates an auto-correlation value of 1, asshown in Equation 4, and a delay not equaling 0 indicates a value of 0.Moreover, the properties where the cross-correlation value is always aprime number is not deteriorated whereby effective correlation ismaintained. Further, additional control information can be transmittedby using the information inputted to the fading unit.

Referring to FIG. 9, the generated CAZAC sequence has length X. Here,the value of X is a largest prime number less than the value of L. Inother words, X is a prime number less than L. Thereafter, the generatedCAZAC sequence having length X has elements added or a padding portionadded to the CAZAC sequence in order to make the length of the generatedCAZAC sequence correspond to the desired length L. Here, C1 representsthe length of the CAZAC sequence having length X, and C2 represents thepadding portion. By combining C1 and C2 (C1+C2), the generated CAZACsequence can have a length corresponding to the desired length L.

FIG. 10 illustrates an exemplary application of circular shift. Thecircular shift is typically applied to increase an amount of controlinformation transmitted to the communication system. For example, a backportion of the sequence is re-allocated to a front portion of thesequence, and the remaining sequence is shifted in the direction of theback portion of the sequence in an amount (or length) corresponding tothe re-allocated back portion, as illustrated in FIG. 10. Further, ifspecified control information is applied the circular shift as describedabove, the amount of control information that can be transmitted via acorresponding sequence increases.

Discussions of above relate to the methods of generating the sequenceusing the desired length L, and of increasing transmitted controlinformation using the circular shift. If these methods are applied ingenerating the sequence, the following processes take place. First,select a smallest prime number greater than L or a largest prime numberless than L, which is referred to as X. Second, remove or add a sequenceunit having a length corresponding to X-L or L-X. Third, apply thecircular shift to the resulting sequence.

FIG. 11 is an exemplary diagram illustrating application of circularshift to the generated code sequence after the elements of the codesequence are removed. Referring to FIG. 11, the code sequence 1102 isgenerated based on length X which is the smallest prime number greaterthan length L. In other words, the generated code sequence 1102 has alength equaling length X which is longer than the desired length L. Fromthe generated code sequence 1102, a portion having a lengthcorresponding to length X-L is removed, resulting in a code sequencehaving length L 1103. Thereafter, the result of the generated codesequence 1103 having length L is applied circular shift thereto,resulting in the code sequence 1104.

FIG. 12 is an exemplary diagram illustrating application of circularshift to the generated code sequence prior to removing the elements ofthe code sequence. In other words, circular shift is performed to thegenerated CAZAC sequence having length X and after circular shift isperformed, the elements of the code sequence are removed.

Referring to FIG. 12, the code sequence 1202 is generated based onlength X which is the smallest prime number greater than length L. Inother words, the generated code sequence 1202 has a length equalinglength X which is longer than the desired length L. A circular shift isthen performed to the generated code sequence 1203 having length X.Thereafter, a portion of the generated code sequence having a lengthcorresponding to length X-L is removed, resulting in a code sequence1204 having length L.

FIG. 13 is an exemplary diagram illustrating application of circularshift to the generated code sequence after a padding portion isattached. Referring to FIG. 13, the code sequence 1302 is generatedbased on length X which is the largest prime number smaller than thevalue of length L. To the generated CAZAC sequence 1302, a paddingportion is added 1303. The length of the padding portion corresponds toa length L-X. As discussed, the padding portion can be comprised ofzeroes or cyclic prefix/postfix. With the addition of the paddingportion, the length of the CAZAC sequence equals the desired length L.Thereafter, the result of the generated code sequence having length L1303 is applied circular shift thereto, resulting in the CAZAC sequence1304.

FIG. 14 is an exemplary diagram illustrating application of circularshift to the generated code sequence prior to attaching a paddingportion. In other words, circular shift is performed to the generatedCAZAC sequence having length X, and after circular shift is performed,the padding portion is attached.

Referring to FIG. 14, the code sequence 1402 is generated based onlength X which is the largest prime number smaller than the value of thedesired length L. To the generated CAZAC sequence 1402, circular shiftis performed. The circularly-shifted CAZAC sequence 1403 still haslength X. To the CAZAC sequence 1403, a padding portion is added,resulting in the CAZAC sequence 1404. The length of the padding portioncorresponds to a length L-X. As discussed, the padding portion can becomprised of zeroes or cyclic prefix/postfix. With the addition of thepadding portion, the length of the CAZAC sequence 1404 equals thedesired length L.

Between FIGS. 11 and 12, the difference is that circular shift isperformed either before or after the elements of the CAZAC sequence areremoved. By performing circular shift before removing the elements (oradjusting the length to equal the desired length), correlationdeterioration can be reduced. To put differently, the CAZAC sequencedoes not have discontinuous codes.

Between FIGS. 13 and 14, the difference is that circular shift isperformed either before or after the padding portion is added to thegenerated CAZAC sequence. By attaching the padding portion afterperforming circular shift, better correlation properties can beattained, especially since the padding portion is placed at the end ofthe code sequence.

Further, according to the discussion above, the desired length L (orrequired length) is first recognized. As illustrated with respect toFIGS. 11-14, the generated code sequence is adjusted/modified based onthe desired length L. Based on that, after the desired length Lrecognized, a determination can be made as to whether the generatedlength X should be shortened or extended. In other words, thedetermination can be made whether to remove or discard at least oneelement of the generated code sequence or to add or insert at least oneelement to the generated code sequence. As discussed, the elements to beinserted can be a null (0) element (e.g., zero padding) or cyclicprefix/postfix, for example. In order to make the determination betweendiscarding the element(s) or adding the element(s), the system canchoose to select the length closest to the desired length L.

For example, if the desired length L is 75, the value of the smallestprime number greater than 75 is 79, and the value of the largest primenumber smaller than the 75 is 73. Here, the prime number 73 can beselected since 73 is closer to 75 than 79 is to 75.

Although the illustration above selects the prime number closest to thedesired length L, selection regarding removal or addition of theelement(s) is not limited to the example of above and otherimplementations may be applied.

Regarding padding, there are five (5) schemes by which padding can beaccomplished. As a first padding scheme, the padding portion can becomprised of a constant number (e.g., 0s). Although the padding portionis used to fill the portion of the code sequence so that the length ofthe code sequence coincides with the desired length, it is possible forthe padding portion to be less then completely full. In other words, itis possible for that the length of the code sequence with padded portionis not equal to or is shorter than the code sequence with the desiredlength. That is, when the code sequence is used for functions deemedless important, such as for cell search or random access, it is notnecessary to use the entire length of the code sequence, and as such,the padding portion does not need to be completely occupied tocorrespond to the desired length of the code sequence.

As a second padding scheme, the padding portion can be comprised of arepeated portion. In other words, the portion corresponding to L-X ofthe code sequence 1204 can be duplicated and inserted/attached to theend of the code sequence 1204. This can be referred to as cyclicpostfix. Here, the code sequence uses the entire length L. Whendetermining the identification (ID) of the code sequence, the entirelength L is used to facilitate identifying of the code sequence ID. Atthe same time, the generated code sequence does not experiencedistortion by using the entire length L. In the discussion above, thecyclic postfix is used. Alternatively, cyclic prefix can also be used.

As a third padding scheme, the padding portion can be comprised ofadditional information through which different messages can bedelivered. More specifically, the desired length L of the code sequencecan be used to generate a supplemental code sequence whose length equalsthe desired length L (N=L). The code sequence portion corresponding toL-X is extracted from the supplemental code sequence andinserted/attached to the generated code sequence as the padded portion.

As a fourth padding scheme, a portion corresponding to length L-X isextracted from the code sequence and inserted as the padding portion.Here, the code sequence inserted to the padding portion may be adifferent code sequence than the code sequence 1204. Put differently,the code sequence inserted to the padding portion may be a CAZACsequence having a length of M, for example, which is different from thecode sequence 1204 having a length of L. Further, the code sequenceinserted to the padding portion can be a different code sequence otherthan the CAZAC sequence. By using different code sequence, additionalinformation can be delivered including information related to type ofcode sequence adjustments.

As a fifth padding scheme, the padding portion can be used as lowerbandwidth guard interval. During transmission of control informationusing a prescribed sequence, the following possible scenarios can occursuch as transmitting data without establishing synchronization with anaccess channel, transmitting data by a plurality of users within acommunication system, and distortion of frequency of the received data.

Furthermore, the padding portions can be placed at both ends of the codesequence to use the padding portions as guard intervals of the lowerbandwidth. Consequently, a more reliable acquisition of controlinformation from the received data can take place despite distortedfrequency signals. In the padding portions used as guard intervals,constant numbers (e.g., 0s) can be used or cyclic prefix or postfix ofthe generated code sequence can be used.

If the padding portions are placed at both ends of the code sequence andused as guard intervals of the lower bandwidth, the code sequences canbe protected from frequency signal distortions. Moreover, if 0s areinserted between the guard intervals or put differently, within the codesequence, interference to neighboring codes can be reduced.Alternatively, if cyclic prefix/postfix is used as guard intervals, thecode sequences can be protected from frequency distortions and can beused to transmit the control information containing the sequence ID ifthere is no frequency distortion.

FIG. 15 is an exemplary diagram of a padding portion of the codesequence in which the padding portion is used as a lower bandwidth guardinterval. Referring to FIG. 15, the code sequence 1501 can be dividedinto three (3) parts—a portion (C1), which is generated based on lengthX, and the other two portions (C2 and C3) are attached to both ends ofthe code sequence 1501.

In the discussions above, five (5) padding schemes are introduced.However, the padding schemes are not limited to the discussed schemes,and there can be other types of padding schemes.

Besides the first padding scheme in which no information is inserted,the other four padding schemes insert additional information in thepadding portions to allow expansion of the code sequence and/ortransmission of message(s). Various information can be inserted into thepadding portion including, for example, initial access information,timing update information, resource request information, user IDinformation, channel quality information (CQI), user group IDinformation related to a random access channel (RACH). Furthermore, theinformation can include cell ID information, multi-input multi-output(MIMO) information, and synchronization channel information of asynchronization channel (SCH), for example. In addition, the paddingportion can be used for transmitting data for message transmission aswell as arbitrary information using a code sequence having a length ofL-X.

FIG. 16 is a structural diagram for transmitting the code sequence.Depending on whether the transmission of the code sequence is made in adownlink direction or an uplink direction, the structure can be indifferent form. With that, FIG. 16 is described with respect to ageneral transmitting end for transmitting the control signal.

Referring to FIG. 16, the transmitting end 1601 comprises a sequenceselection unit 1602 and a transmitting unit 1603. The sequence selectionunit 1602 is used to generate the code sequence for transmitting thecontrol information. More specifically, the sequence selection unit 1602performs an operation to select a code sequence having a desired lengthof L. In other words, the sequence selection unit 1602 stores the valueof the desired length L, and then selects an appropriate code sequencefor expressing the control information to be transmitted where the codesequence has a length of L.

The code sequence that can be selected by the sequence selection unit1602 has a length of L as illustrated in FIGS. 12 and 14 (e.g., codesequence 1204 and code sequence 1404). Moreover, the code sequence isapplied circular shift (e.g., code sequences 1203 and 1403) to which apadded portion corresponding to lengths L-X or X-L is removed orinserted/added. As a result, discontinuous parts are not formed withinor in the code sequence to promote superior correlation characteristics.

Although it is preferable to use length X which is a smallest primenumber greater than the length of L or a largest prime number smallerthan the length of L, as long as the value of length X is a primenumber, different or other prime numbers can be used as the value oflength X.

FIG. 17 is a structural diagram illustrating a basic code sequencegeneration unit and a code sequence length adjustment unit. In FIG. 17,the basic code sequence generation unit 1701 further comprises a codesequence generation unit 1701 a and a circular shift application unit1701 b. The code sequence generation unit 1701 a is used to generate afirst code sequence (C1). Here, C1 can be defined as a code sequencehaving a length of X where the value of length X is a smaller primenumber larger than the value of length L or a code sequence having alength of X where the value of length X is a larger prime number smallerthan the value of length L. C1 is then applied circular shift by thecircular shift application unit 1701 b. More specifically, the circularshift application unit 1701 b receives C1 having length of X appliescircular shift, and outputs a second code sequence (C2) to the codesequence length adjustment unit 1702.

The code sequence length adjustment unit 1702 further comprises acontrol unit 1702 a, a code sequence removing unit 1702 b, and a paddingunit 1702 c. More specifically, the control unit 1702 a receives C2 aswell as the value of length L. The control unit 1702 a determineswhether to remove a portion/section of C2 or insert/add aportion/section to C2. Based on the determination from the control unit1702 a, C2 is delivered to the sequence removing unit 1702 b in which aportion/section of C2 corresponding to a length of X-L is removed.Alternatively, C2 can be delivered to the padding unit 1702 c forinserting/adding a portion/section of C2 whose length corresponds to thelength of L-X.

If C2 and the value of length L are provided to the control unit 1702 a,the control unit 1702 a compares the value of length X which identifiesthe length of C2 with the value of the length L. Here, if X is greaterthan L, then C2 is inputted into the sequence removing unit 1702 b. FromC2, the portion length of C2 corresponding to length X-L is removed,resulting in C3. However, if X is less than L, then C2 is inputted intothe padding unit 1702 c. From C2, the padding portion lengthcorresponding to length L-X is inserted/added to C2, resulting in C4.Here, the padding portion can be inserted to either end or both ends ofC2.

FIGS. 18 and 19 illustrate cross-correlation characteristics of the codesequence. The illustrations of FIGS. 18 and 19 is based on the value oflength X being the smallest prime number greater than the value of thedesired length L; however, the illustrations are not limited to thesmallest prime number greater than length L but can have a prime numbervalue of length X smaller than the value of length L.

Referring to FIGS. 18 and 19, the x-axis represents values of circularshift while the y-axis represents un-normalized cross-correlationvalues. Furthermore, a thinner line represents the value ofcross-correlation of the code sequence with circular shift appliedthereto after a code sequence portion having the length X-L is removed.A darker/thicker line represents values of code sequence to whichcircular shift is applied prior to removing the code sequence portioncorresponding to the length X-L. More specifically, FIG. 7 illustrates agraph where L is 75 and X is 79 which is the smallest prime numbergreater than 75. Moreover, FIG. 8 illustrates a graph where L 8 is 225and X is 227 which is the smallest prime number greater than 225.

In FIGS. 18 and 19, if the value of circular shift is 0 or putdifferently, if there is no shift, then high correlation value isindicated only when the auto-correlation value of the code sequencecorresponds and in other cases, moderate correlation is maintained. Onthe contrary, if the code sequence has a section corresponding to lengthX-L is removed and thereafter applied circular shift, severefluctuations occur with correlation values, resulting in deterioratedcorrelation characteristics. As such, if cross-correlation is used toanalyze the code sequence, the code sequence according to theembodiments of the present invention shows superior performance andoutcome to that of the conventional code sequence.

FIG. 20 is an exemplary diagram illustrating boosting the power of thegenerated code sequence. As discussed, the code sequence is generatedbased on length X, and a padding portion, whose length corresponds tolength L-X is attached to the code sequence (e.g., CAZAC sequence).Thereafter, the portion of the code sequence corresponding to length Xis used where length L is divided by length X (L/X). The result of thedivision is the amount of power that can be boosted. Moreover, theamount of power that can be boosted can be applied to the code sequencewhose length is length X. When the receiving end receives power boostedcode sequence, more effective detection performance can be achievedsince interference is reduced.

However, regarding a code sequence generated with a padding portion withcyclic prefix/postfix attached thereto, there is no need to power boostsince all of the code sequences corresponding to length L are used foracquiring sequence ID information.

In the receiving end, information related to the generated code sequenceand length X used to generate the code sequence is received. From thecode sequence, a portion corresponding to length X is processed toacquire the control information. To this end, it is important to firstreceive synchronization information of the received data. Equation 7 andEquation 8 can be used to acquire synchronization information. Here,Equation 7 relates to auto-correlation, and Equation 8 relates tocross-correlation.

$\begin{matrix} {{{{R_{M:N}(d)} = {\sum\limits_{k = 0}^{X - 1}{{c( {k,M,X} )} \cdot {c^{*}( {{{mod}( {k + d} )},X} )}}}};M},X} ) & \lbrack {{Equation}\mspace{14mu} 7} \rbrack \\ {{{{R_{M_{1}:{M_{2}:N}}(d)} = {\sum\limits_{k = 0}^{X - 1}{{c( {k,M_{1},X} )} \cdot {c^{*}( {{{mod}( {k + d} )},X} )}}}};M_{2}},X} ) & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Equation 7 is used to acquire auto-correlation value(s) from thereceived code sequence whose sequence ID is M. Further, the acquiredauto-correlation value d, which is a value other than 0, is used toachieve synchronization.

Equation 8 is used to acquire cross-correlation value(s) of a codesequence whose ID is M₂ from the received code sequence whose sequenceID is M₁. Through the acquired value, synchronization can be achieved.

Typically, if the wireless communication system is a synchronousnetwork, auto-correlation is used to acquire synchronizationinformation, and if the system is an asynchronous network,cross-correlation is used to acquire synchronization information.However, according to the embodiments of the present invention,synchronization information can be acquired using any one or at leastone of the correlation schemes.

After the synchronization information of the received code sequence isacquired, the receiving end analyzes the received code sequence toacquire the sequence ID, as shown in Equations 9 and 10.σc(k;M,X)=c(k+1;M,X)·c*(k;M,X)(for k=0,1, . . . , L−1)  [Equation 9]σc(k;M,X)=c(k+1;M,X)·c*(k;M,X)(for k=0,1, . . . , X−1)  [Equation 10]

In Equations 9 and 10, σc(k; M,X) denotes difference sequence of thereceived sequences. Equation 9 is used to acquire the ID information ofthe received sequence using the differential sequence corresponding tothe total length of the received sequence. Equation 9 can also be usedto acquire the ID information of the code sequence which has beengenerated with the cyclic prefix/postfix padded portion. Equation 10 isused to acquire the ID information of the received sequence using thesmallest prime number corresponding to length X.

As discussed, if the differential sequence of the CAZAC sequence iscalculated using Equations 9 or 10, k of the sequence index isgenerated, and the result therefrom is transformed by the Fouriertransform scheme, to show a single peak value. Thereafter, by detectingthe peak value, the ID information of the sequence can be acquired.

The discussion of above regarding a code sequence or a code sequence setcan be applied to 3^(rd) Generation Partnership Project (3GPP) system or3GPP2 system as well as a Wibro system or a Wimax system.—

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for transmitting a synchronization channel (SCH) signal bygenerating a code sequence in a wireless communication system, themethod comprising: generating a first code sequence (C₁) having a firstlength by using a first variable (M₁); generating a second code sequence(C₂) having a second length by using a second variable (M₂), wherein theM₁ and the M₂ are different from each other; generating the codesequence as a combination of the first code sequence (C₁) and the secondcode sequence (C₂); and transmitting the code sequence as the SCHsignal, wherein at least one of the first length and the second lengthis a prime number length, and the sum of the first length and the secondlength corresponds to a length of the SCH signal, wherein thecombination of the first code sequence (C₁) and the second code sequence(C₂), each of which is generated using the different variables, providesa receiving end device with information about a cell identification anda location of the SCH within a radio frame.
 2. An apparatus fortransmitting a synchronization channel (SCH) signal by generating a codesequence in a wireless communication system, the apparatus comprising: acode sequence generating module for generating a first code sequence(C₁) having a first length by using a first variable (M₁), generating asecond code sequence (C₂) having a second length by using a secondvariable (M₂), wherein the M₁ and the M₂ are different from each other,and generating the code sequence as a combination of the first codesequence (C₁) and the second code sequence (C₂); and a transmissionmodule for transmitting the code sequence as the SCH signal, wherein atleast one of the first length and the second length is a prime numberlength, and the sum of the first length and the second lengthcorresponds to a length of the SCH signal, wherein the combination ofthe first code sequence (C₁) and the second code sequence (C₂), each ofwhich is generated using the different variables, provides a receivingend device with information about a cell identification and a locationof the SCH within a radio frame.
 3. A method for receiving asynchronization channel (SCH) signal by using a code sequence in awireless communication system, the method comprising: receiving the codesequence as the SCH signal in a form of a combination of a first codesequence (C₁) having a first length, which has been generated by using afirst variable (M₁), and a second code sequence (C₂) having a secondlength, which has been generated by using a second variable (M₂),wherein the M₁ and the M₂ are different from each other; and acquiringinformation about a cell identification and a location of the SCH withina radio frame via the combination of the first code sequence (C₁) andthe second code sequence (C₂), wherein at least one of the first lengthand the second length is a prime number length, and the sum of the firstlength and the second length corresponds to a length of the SCH signal.